The present invention relates to electrical interconnections, methods of conducting electricity, and methods of reducing horizontal conductivity within an anisotropic conductive adhesive.
Integrated circuitry is utilized in an ever-increasing number of applications. To meet the needs of the expanding applications, new methods of packaging integrated circuits and connecting integrated circuits with other substrates or circuitry have been developed. Various factors must be considered when connecting integrated circuitry with an adjoining substrate or circuit. Such factors include reliability, performance or speed, and size requirements to meet the requirements of higher definition sub-micron integrated circuits.
Conventional circuit interconnections include flip chip bonding, tape automated bonding (TAB) and conventional wire bonding. Flip chip bonding is preferred in rapid communication or high performance applications because shorter signal paths are provided. The pads are provided upon one surface of the flip chip and the pads can be aligned with conductive pads on an opposing substrate for interconnection. Solder or some type of adhesive is typically used to couple the flip chip with the substrate.
Anisotropic conductive adhesives (ACA) including anisotropic conductive film (ACF) and anisotropic conductive paste (ACP) are used for fine pitch interconnections. These interconnections are utilized in exemplary applications including liquid crystal display (LCD) panels, tape carrier packages (TCP), printed circuit board (PCB) interconnections, indium tin oxide (ITO) connections, and flexible circuit substrate connections.
Such anisotropic conductive adhesives typically comprise an adhesive matrix and plural conductive particles within the adhesive matrix. The conductivity of the anisotropic conductive adhesive is determined by the weight percentage of the conductive fillers or number of conductive particles per unit area. The conductive particles are is randomly distributed throughout the adhesive matrix in conventional anisotropic- conductive adhesives.
Referring to FIG. 1, plural substrates 1, 2 are shown having respective opposing bond pads 3, 4. An anisotropic conductive adhesive 5 is applied intermediate substrates 1, 2. Anisotropic conductive adhesive 5 includes plural conductive particles 6. One conductive particle 6 intermediate bond pads 3, 4 provides electrical coupling of bond pads 3, 4.
Benefits of anisotropic conductive adhesives include the ability to provide electrical conduction in a z-axis or a vertical direction (i.e., intermediate bond pads 3, 4) while providing substantial electrical insulation in horizontal directions (i.e., insulate adjacent bond pads of the substrate). High definition- technologies require additional conductive particles (i.e., higher density of anisotropic conductive adhesives) to properly electrically connect all interconnections and bond pads of the devices being connected. Current density passing through the interconnection can be defined by the loading or density of particles in a given volume of the adhesive film and by the surface area of the interface coupling the contacts. Increasing the number of conductive particles results in increased current density.
However, increasing the number of conductive particles within the adhesive films also enhances the chances that the anisotropic conductive adhesive will be conductive in at least one horizontal direction. Such horizontal conduction can lead to short circuits and improper circuit performance.
Therefore, there exists a need to provide interconnections for fine pitch or high definition components without the drawbacks associated with the prior art devices and methodologies.
The present invention includes electrical interconnections, methods of conducting electricity and methods of reducing horizontal conductivity within an anisotropic conductive adhesive.
According to one embodiment, an electrical interconnection is configured to electrically couple a first substrate and a second substrate. The electrical interconnection includes plural electrical contacts. The contacts comprise bond pads of the respective substrates in one embodiment.
An electrical contact of the first substrate has a male configuration and an electrical contact of the second substrate has a female configuration in a preferred embodiment. The electrical contacts of the first and second substrates are configured to mate or couple to form an electrical interconnection. In one embodiment, the male configuration is convex and the female configuration is concave. At least a portion of the male configuration is preferably received within the female configuration during mating.
Other mating configurations can be utilized to form the electrical interconnection. The mating configurations are used to align or guide the substrates during coupling of the substrates in one embodiment.
In some embodiments, an adhesive is provided intermediate the electrical contacts of the electrical interconnection. One exemplary adhesive includes plural conductive particles for providing electrical coupling intermediate the electrical contacts. Such an adhesive comprises an anisotropic conductive adhesive configured to conduct electricity in a vertical direction. Anisotropic conductive adhesives are also configured to provide substantial electrical isolation in horizontal directions. The adhesive can be provided intermediate both substrates during coupling of the substrates.
The electrical contacts of one disclosed electrical interconnection are coupled at an interface. The electrical contacts are preferably configured to provide increased surface area at the interface. The surface area of the interface is ideally greater than a planar dimension defined by the electrical contacts.
Such an interface of increased surface area permits coupling of electrical contacts via an increased number of conductive particles within the adhesive. This configuration reduces resistance within the electrical interconnect. In addition, an anisotropic conductive adhesive having reduced conductive particle loading can be utilized in such configurations while maintaining a substantially similar vertical conductivity intermediate the electrical contacts. Anisotropic conductive adhesives having reduced conductive particle loading provide reduced horizontal electrical conduction and increased insulation of adjacent electrical interconnects.